In the printing field, the impact type printer has been the predominant apparatus for providing increased throughput of printed information. The impact printers have included the dot matrix type wherein individual print wires are driven from a home position to a printing position by individual and separate drivers. The impact printers also have included the full character type wherein individual type elements are caused to be driven against a ribbon and paper or like record media adjacent and in contact with a platen.
The typical and well-known arrangement in a printing operation provides for transfer of a portion of the ink from the ribbon to result in a mark or image on the paper. Another arrangement includes the use of carbonless paper wherein the impact from a print wire or a type element causes rupture of encapsulated material for marking the paper. Also known are printing inks which contain magnetic particles wherein certain of the particles are transferred to the record media for encoding characters in manner and fashion so as to be machine readable in a subsequent operation. One of the known encoding systems is MICR (Magnetic Ink Character Recognition) utilizing the manner of operation as just mentioned.
While the impact printing method has dominated the industry, one disadvantage of this type of printing is the noise level which is attained during printing operation. Many efforts have been made to reduce the high noise levels by use of sound absorbing or cushioning materials or by isolating the printing apparatus.
More recently, the advent of thermal printing which effectively and significantly reduces the noise levels has brought about the requirements for heating of extremely precise areas of the record media by use of relatively low energy, thin film resistors or like thermal print head elements. The intense heating of the individually isolated elements causes transfer of coating material from a coated medium onto paper or like receiving substrate. Alternatively, the paper may be of the thermal type which includes materials that are responsive to the generated heat.
The use of thermal transfer printing, especially when performing a subsequent sorting operation, can result in smearing or smudging adjacent the printed symbols or digits on the receiving substrate. This smearing can make character recognition, such as OCR (Optical Character Recognition) or MICR (Magnetic Ink Character Recognition), difficult and sometimes impossible. Additionally, the surface of the receiving substrate and the printed symbols or digits are subject to scratching which can result in blurred images and also result in incorrect reading of the characters. Further, it has been found that certain transfers of coating material from the coated medium to the receiving substrate resulted in ill-defined and non-precise or blurred images.
In the case of previous or prior art formulations used in thermal printing technology and still in use today, solvent or hot melt systems involve the use of temperatures of 150-300 degrees F. The hot melt process uses waxes and resins along with pigments which are formulated at temperatures of 150-300 degrees F. The solvent process uses volatile solvents incorporating waxes, resins and pigments which are formulated at temperatures of 150-170 degrees F. However, there is an environmental problem with disposal of excess materials when using these processes.
Still more recently, the environment has become a controversial issue in the matter of awareness and protection of certain areas, and means are being implemented to protect such areas. One of the means for protecting the environment is reducing the emissions of volatile organic compounds (VOC) in manufacturing processes. In this regard, it is expected that the use of synthetic solvents will be eliminated or substantially reduced within a few years.
In view of these environmental issues and the conditions associated therewith, the present invention has resulted in a thermal transfer medium in the preferred form of a ribbon which eliminates or substantially reduces smearing or smudging and scratching across or adjacent the printed digits or symbols during sorting or other operations, and the ribbon is made of materials that are acceptable by the industry for environmental protection.
Hundreds of formulations and many more compounds were used in water base experimental operations to find an optimum coating for use in thermal printing technology that is environmentally acceptable. The present invention uses water and a small amount of volatile solvent to create a coating that is acceptable, the solvent being included for proper rheological control.
Representative documentation in the area of nonimpact printing includes U.S. Pat. No. 3,663,278, issued to J. H. Blose et al. on May 16, 1972, which discloses a thermal transfer medium having a coating composition of cellulosic polymer, thermoplastic resin, plasticizer and a sensible dye or oxide pigment material.
U.S. Pat. No. 4,315,643, issued to Y. Tokunaga et al. on Feb. 16, 1982, discloses a thermal transfer element comprising a foundation, a color developing layer and a hot melt ink layer. The ink layer includes heat conductive material and a solid wax as a binder material.
U.S. Pat. No. 4,343,494, issued to G. H. Ehrhardt et al. on Aug. 10, 1982, discloses a carbonless copy paper with a hot melt coating on one surface and an image receptor coating on the other surface.
U.S. Pat. No. 4,347,282, issued to G. H. Ehrhardt et al. on Aug. 31, 1982, discloses a chemical carbonless copy paper with a hot melt coating.
U.S. Pat. No. 4,403,224, issued to R. C. Wironwski on Sept. 6, 1983, discloses a surface recording layer comprising a resin binder, a pigment and a smudge inhibitor dispersed in the binder.
U.S. Pat. No. 4,463,034, issued to Y. Tokunaga et al. on Jul. 31, 1984, discloses a heat sensitive magnetic transfer element having a hot melt or a solvent coating.
U.S. Pat. No. 4,523,207, issued to M.W. Lewis et al. on Jun. 11, 1985, discloses a thermal record sheet which uses crystal violet lactone and a phenolic resin.
U.S. Pat. No. 4,592,954, issued to S. L. Malhotra on Jun. 3, 1986, discloses a transparency for ink jet printing and having a substrate and a coating consisting essentially of a blend of carboxymethyl cellulose and polyethylene oxides.
U.S. Pat. No. 4,628,000, issued to S. G. Talvalkar et al. on Dec. 9, 1986, discloses a thermal transfer formulation that includes an adhesive-plasticizer or transfer agent and a coloring material or pigment.
U.S. Pat. No. 4,651,177, issued to S. M. Morishita et al. on Mar. 17, 1987, discloses a thermal transfer recording material having a heat-meltable ink layer comprising a dye or pigment, a binder and a wax which are coated on a support as an aqueous solution and/or an aqueous emulsion.
U.S. Pat. No. 4,687,701, issued to F. Knirsch et al. on Aug. 18, 1987, discloses a heat-sensitive inked element using a blend of thermoplastic resins and waxes.
U.S. Pat. No. 4,688,057, issued to S. Ueyama on Aug. 18, 1987, discloses a heat-sensitive transferring recording medium with an ink layer consisting essentially of three waxes of different values, an extender pigment and a coloring agent.
U.S. Pat. No. 4,707,395, issued to S. Ueyama et al. on Nov. 17, 1987, discloses a substrate, a heat-sensitive releasing layer, a coloring agent layer, and a heat-sensitive cohesive layer.
U.S. Pat. No. 4,777,079, issued to M. Nagamoto et al. on Oct. 11, 1988, discloses an image transfer type thermosensitive recording medium using thermosoftening resins and a coloring agent.
U.S. Pat. No. 4,778,729, issued to A. Mizobuchi on Oct. 18, 1988, discloses a heat transfer sheet having a hot melt ink layer on one surface of a film and a filling layer laminated on the ink layer.
U.S. Pat. No. 4,792,495, issued to M. Taniguchi et al. on Dec. 20, 1988, discloses a fusible ink sheet having a top layer of carnauba wax, montan wax or paraffin wax and ethylene vinyl acetate copolymer on a color layer.
U.S. Pat. No. 4,882,218, issued to K. Koshizuka et al. on Nov. 21, 1989, discloses a thermal transfer recording medium having two heat softening layers each containing a polyoxyethylated compound.
U.S. Pat. No. 4,956,225, issued to S. L. Malhotra on Sep. 11, 1990, discloses a transparency suitable for imaging and having a polymeric substrate with a toner receptive coating on one surface and which coating is comprised of blends selected from the group consisting of polyethylene oxide, carboxymethyl cellulose and hydroxypropyl cellulose.
U.S. Pat. No. 5,021,291, issued to T. Kobayashi et al. on Jun. 4, 1991, discloses an ink-bearing medium comprising a water-soluble resin containing polyvinyl alcohol, a fusible ink material containing a solid fatty acid, a coloring agent, and a fusible agent.
U.S. Pat. No. 5,045,383, issued to M. Maeda et al. on Sep. 3, 1991, discloses a thermosensitive image transfer recording medium comprising a support, a release layer having an unvulanized rubber and a thermofusible wax component and a thermofusible ink layer having a coloring agent and a thermofusible resin component.
And, U.S. Pat. No. 5,128,308, issued to S. G. Talvalkar on Jul. 7, 1992, discloses a thermal transfer ribbon comprising a substrate, a first coating thereon containing water-based ingredients which are thermally reactive for creating color images, the ingredients being a leuco dye and a phenolic resin, and a second coating containing solvent-based ingredients which are thermally active for transferring the color images.